Fine Homebuilding magazine had a review of 18 volt combo kits in the January 2006 issue. From their article:
Best Overall Choice - Milwaukee. Power:A-, Endurance:A, Controls/Adjustments:A+, Battery/Charger:B+
Best Value Choice - DeWalt. Power:A+, Endurance:B+, Controls/Adjustments:B+, Battery/Charger: C+
Ridgid, Porter Cable, and Bosch were listed as very good tools that would be recommended.
Metabo and Makita ranked behind the recommended group.
Panasonic, Hitachi, Craftsman, and Ryobi not recommended for a variety of reasons. The main reason was that they did not offer value for the money.
This article was written before the new Makita 18 Volt LXT Lithium Tools or Milwaukee V18 Lithium batteries (tools are basically same as with NiCad battery packs) were widely available. I've heard nothing but good things about the Makita LXT tools.
The DeWalt 18 volt platform is by far the most versatile with over 30 tools available. Around here, Dewalt dominates the 18 volt market for commercial construction. Milwaukee is a distant second. You see a small mix of everything else.
As far as the reconditioned tools go, the tools themselves are usually perfectly fine. What you have to watch out for is the batteries. The batteries that come with reconditioned tools are used and may or may not have a long life ahead of them. Replacement is pricey unless you can convince the vendor to give you new batteries.
I think your best bet is to go to a dedicated tool store and handle the main tools from each kit that you are considering and see what you do or don't like.
If you're willing to buy without handling each kit, check out
Heavy Duty Tools. They have good prices and give awesome service. The only problem is that their stock moves quickly and sales disappear as soon as items sell out.